The present invention is directed to the aqueous cleaning of spin coating bowl assemblies employed in microelectronic fabrication processes. This invention is particularly concerned with the cleaning of photoresist, polyimide and other polymers from spin coating bowl assemblies with water based detergent compositions as an environmentally friendly replacement of organic solvents that are commonly used for cleaning photoresist and polyimide residue from polymer film application equipment. The invention is also applicable to cleaning low dielectric constant polymer dielectric residue from spin coating bowls and associated equipment for coatings on device wafers and on ceramic substrates.
In semiconductor device fabrications, formation of thin polymer films of photoresist, antireflective coatings, polyimide-polyamic acid precursor, and low dielectric constant polymer dielectric materials (low-k materials) such as Silk (Dow trade name), and siloxane based materials such as silsesquioxane and hydrogen silsesquioxane (HSQ) polymers on various substrates by the spin coating technique is an important part of the process sequence. Various solvents used in film coating formulations of these polymers include: propyleneglycol methylether acetate (PGMEA), cyclohexanone, ethoxyethyl propionate (EEP), ethyl lactate, methyl isobutyl ketone (MIBK), n-methylpyrrolidinone (NMP), gama-butyrolactone, aromatic hydrocarbons and mixture thereof. The spin coating equipment includes a coating bowl assembly made of a machined teflon top shield, a stainless steel plate, and a bottom teflon bowl. The substrate, silicon wafer or ceramic substrate to be coated is positioned on a vacuum chuck in the center of the bowl where it is held in place by vacuum during spinning. A small volume of the polymer solution is dispensed in the center of the substrate and spun at a pre-determined spin speed and time duration. In this operation, excess polymer solution which may be a photoresist, typically comprising a phenolic resin of the type novolak or poly (p-hydroxystyrene) as matrix resins and a photoactive compound, acid-amplified resists, antireflective coating formulation, polyimide-polyamic acid coating formulation, or low-k polymer materials, splashes against the inside walls of the spin coating bowl and other assembly parts. Although most of the excess polymer drains into a receptacle from where it is later removed, a fraction of the splashed material remains adhered to the spin coater walls and associated assembly parts. With repeated use of the spin coating bowl assembly, the polymer builds up inside the coater bowl and the assembly parts to several hundred microns which, if not removed, can flake off causing contamination on the film surface, film defects and consequently product yield loss. Therefore, it is essential to clean the spin coating bowl assembly every 100 to 200 hours of use to prevent the possibility of film defects caused by falling debris of dry polymer residue.
At present, throughout the microelectronic industry, the resist coating bowls and associated equipment are cleaned with organic solvents, typically, 1-methyl-2-pyrrolidinone (NMP), n-butyl acetate (nBA), acetone, isopropanol (IPA), methyl isobutylketone (MIBK) and dimethylacetamide (DMAC). As such organic solvents may present environmental problems, it is necessary to install specialized abatement equipment to control air emissions. In addition to environmental problems, IPA, nBA, MIBK and acetone are highly flammable solvents having flash point less than 100xc2x0 F. and thus present a fire hazard, which requires costly explosion-proof equipment for their use.
There are a number of methods proposed by others for the stripping and cleaning of photoresist and polyimide residues. Nishi, Japanese Patent number 08104895, the disclosure of which is incorporated by reference herein, discloses the use of diacetone alcohol for cleaning photoresist based on quinonediazide-novolak.
Sugyama, Japanese Patent number 08165495, the disclosure of which is incorporated by reference herein, discloses a solvent system comprising a mixture of 1-methyl-2-pyrrolidinone and/or N, N-dimethylacetamide, and alkylene glycol monoalkyl ethers for cleaning polyimide precursor residues in semiconductor manufacturing.
Walsh et al. U.S. Pat. No. 5,698,045, the disclosure of which is incorporated by reference herein, discloses a method for removing polymer residue from chemical processing equipment according to which the contaminated surface is exposed to vapors of NMP such that the vapors from the boiling solvent condense on the polymer surface causing the polymer to flake-off.
Notwithstanding the prior art, major problems with the cleaning solvents for photoresist and polyimide residues disclosed in the art are chemical safety, and environmental concerns. Thus, a purpose of the present invention is to have a method for providing suitable water-based cleaning alternatives along with the necessary cleaning equipment for aqueous cleaning processes.
Accordingly, it is a purpose of this invention to provide an environmentally friendly water-based cleaning method for cleaning polymer residues of photoresist, antireflective coatings, siloxane containing polymers, polyimide, spin-on low k interlevel dielectric polymer and the like from spin coating bowl assemblies and replace organic solvents such as NMP, IPA, acetone, nBA, MIBK, diacetone alcohol etc., which are traditionally used for cleaning polymer residue from various surfaces in semiconductor device manufacturing.
It is another purpose of this invention to provide water-based detergent formulations for spin coater bowl assembly cleaning employing a combination of surfactants in conjunction with alkali, alkanolamine, and alkali metal salt of dibasic/polybasic organic acid.
It is another purpose of this invention to provide a polymer coater bowl cleaning unit assembly and method for spin coater bowl assembly cleaning with aqueous detergent formulations employing ultrasonic cleaning and a dishwasher rinse cycle.
It is another purpose of this invention to provide aqueous cleaning solutions for polymer processing equipment in semiconductor manufacturing using water solution of surface tension lowering agents in conjunction with alkali metal hydroxides, or tetraalkyammonium hydroxide, alkanolamine, and combinations thereof.
It is another purpose of this invention to provide a method for aqueous cleaning of spin coater bowl assembly and related polymer processing equipment.
It is another purpose of this invention to provide an aqueous cleaning method for polymer spin coating equipment using water-based alkaline solutions which have no problem of volatile air emissions, no chemical safety or flammability issues, and which does not require high cost cleaning equipment.
These and other purposes of the present invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.
This invention is concerned with spin coater bowl assembly cleaning to remove polymer residue of photoresists, antireflective coatings, polyimide precursor coatings, and the low dielectric constant polymers from the spin coating bowl side walls and assembly parts. Particularly, this invention is concerned with replacement of NMP and flammable solvents with water-based cleaning solutions to provide an environmentally friendly option for cleaning spin coating bowl assemblies. This invention is especially concerned with aqueous alkaline cleaning compositions and method of using the same for cleaning polymer spin coating bowls and associated assembly parts to remove polymer residues from coating formulations of photoresists, antireflective coatings, acid-amplified resists, silicone-containing polymers, polyimide-precursor formulations, as well as spin-on low-k materials based on hydrogen silsesquioxane (HSQ), FOx flowable oxide, and related silsesquioxane polymers.
The inventors have discovered that water-based alkaline detergent solutions comprising a combination of surfactants in conjunction with alkanolamine, alkali metal hydroxide, and alkali metal carboxylate salt are highly effective in removing polymer residue, particularly, novolak-diazonaphthoquinone based photoresist, acid-amplified resist, silicone-containing polymers, and polyimide precursor residue from various surfaces including metal, teflon, PFA, polypropylene and other plastics. The aqueous cleaning compositions according to this invention typically comprise about 1% to about 10% (wt %) of active ingredients in water which include a surface active agent, preferably comprising a mixture of a non-ionic surfactant and an amphoteric surfactant and/or an ionic surfactant, alkanolamine, sodium hydroxide, potassium hydroxide, and/or a tetraalkyl ammonium hydroxide, alkali metal salt of a polybasic organic acid, and optionally a corrosion inhibitor. It is found that coater bowl cleaning can be readily effected by ultrasonic agitation in the aqueous alkaline cleaning solution comprising these components, heated to 120xc2x0 F. to 150xc2x0 F. or higher, if the polymer deposit is not dried out or by a static pre-soak followed by ultrasonic agitation in the case of heavy dried out polymer residue.
The water based alkaline detergent solution comprises at least one alkali metal hydroxide, at least one alkanolamine, at least one combination of a non-ionic surfactant and an amphoteric surfactant, and at least one salt of a polybasic organic acid, in water. The water based alkaline detergent solution comprises at least one tetraalkylammonium hydroxide, at least one alkanolamine, at least one combination of a non-ionic surfactant and an amphoteric surfactant, and at least one salt of a polybasic organic acid, in water.
The polymer residue is a low dielectric constant polymer coating formulation selected from the group consisting of silsesquioxane polymer, hydrogen silsesquioxane polymer, flowable oxide polymer and mixtures thereof
The alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof The tetraalkammonium hydroxide is selected from the group consisting of tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, 2-hydroxyethyltrimethyl ammonium hydroxide, and mixture thereof the non-ionic surfactant is selected from the group consisting of ethoxylated alkyl phenols, poly(oxyethylene) dodecyl ether, biodegradable graft co-polymers from mono or oligosaccharides, glucosamides, and mixtures thereof the ethoxylated alkyl phenols are poly(oxyethylene-oxypropylene) nonylphenyl ether or ethoxylated alkyl phenols are poly(oxyethylene-oxypropylene) octylpheny ether. The amphoteric surfactant is selected from the group consisting of coco-imidopropyl betaine, sodium alkoxypropyl iminodipropionate, methylalkyl imidazoline sodium salt and mixtures thereof
The salt of a polybasic organic acid, when used in conjunction with an alkali metal hydroxide, is selected from the group consisting of sodium gluconate, tetramethylammonium gluconate, sodium tartrate, tetramethylammonium tartrate, sodium citrate, potassium citrate, alkali metal salt of polyacrylic acid and mixture thereof
The salt of a polybasic organic acid, when used in conjunction with a tetraalkylammonium hydroxide, is a tetramethyl ammonium carboxylate of organic acid selected from the group consisting of gluconic acid, tartaric acid, citric acid and polyarcylic acid.
The water based alkaline detergent solution, when used in conjunction with an alkali metal hydroxide, further comprises a corrosion inhibitor, a chlorine bleach compound or a combination thereof.
The water based alkaline detergent solution, when used in conjunction with an alkali metal hydroxide, further comprises an alkali metal salt selected from the group consisting of sodium metasilicate, potassium metasilicate, sodium tripolyphosphate, sodium carbonate, potassium carbonate, sodium sesquicarbonate, tetramethylammonium metasilicate, alkanolammonium metasilicate, and mixture thereof
The alkanolamine is selected from the group consisting of ethanolamine, isopropanolamine, n-methylethanolamine, and mixture thereof the alkanolamine may be diethanolamine, triethanolamine, diethylene glycolamine, and mixtures thereof.
The water based alkaline detergent solution constitutes from about 1 weight percent to about 10 weight percent as active ingredients in water to provide a pH in the range from about 11.5 to about 14.0. The active ingredients consist of a mixture of an alkali metal hydroxide, an alkanolamine, a blend of non-ionic surfactant and amphoteric surfactant, and a polybasic organic acid salt in water.
The non-ionic surfactant is selected from the group consisting of ethoxylated alkyl phenols, biodegradable ethoxylated long chain linear alcohols, fluroalky ether surfactants, alkyl-polyglycosides and glucosamides of the lauryl n-methyl glucosamide. The ethoxylated alkyl phenols are selected from the group consisting of poly (oxyethylene-oxypropylene) nonyl phenyl ether and poly(oxyethylene)octylphenyl ether. The biodegradable ethoxylated long chain linear alcohols are selected from the group consisting of poly (oxyethylene) dodecyl ether, and poly (oxyethylene) sorbitan stearates.
The water based alkaline detergent solution further comprises an ionic surfactant selected from the group consisting of alkyl benzene sulfonic acid sodium salt, alkyl benzene sulfonic acid ammonium salt and ammonium salt. The ammonium salt is selected from the group consisting of dodecylbenzene sulfonic acid-sodium salt, dodecylbenzene sulfonic acid diethanolamine salt and triethanolamine salt. The ionic surfactant constitutes from about 0.05 weight percent to about 0.3 weight percent as active ingredients in said water based alkaline detergent solution.
Unlike organic solvent based cleaning methods described in the prior art, the aqueous cleaning method of this invention provides an environmentally safer option that has no problem of volatile air emissions and that poses no chemical safety issue associated with flammable solvents.